Recently, a light emitting diode (LED) is spotlighted as a light emitting device. Since the LED can convert electric energy into light energy with high efficiency and long life span of about 5 years or more, the LED can remarkably reduce the energy consumption and repair and maintenance cost. In this regard, the LED is spotlighted in the next-generation lighting field.
In the LED, a buffer layer is formed on a growth substrate including Si, SiC, or sapphire having a hexagonal crystal structure, and a light emitting semiconductor layer including a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer is formed on the buffer layer. The LED may include a group-III nitride single crystalline semiconductor, and the active layer emits light according to current applied through the first and second conductive semiconductor layers.
Meanwhile, in the LED, due to the difference in a refractive index between the light emitting semiconductor layers including a group III nitride-based semiconductor and air, the light emitted from the active layer is not extracted to the outside, but totally-reflected so that the light is extinguished inside the light emitting semiconductor layer.
Accordingly, in the LED, the light emitted from the active layer has to be extracted to the outside as much as possible to increase energy conversion efficiency (lm/W) of the LED.